It has been proposed to employ a parallelogram type of wheel suspension for the driving wheel of a motorcycle providing an effective swing arm axis which is coincident with the axis of the driving sprocket. One example of such a parallelogram linkage is disclosed in the Buell U.S.A. Pat. No. 4,058,181, issued Nov. 15, 1977. In said prior patent, the suspension linkage includes two pairs of swing arms or links, one pair at each side of the drive wheel, and having swing arm pivots above and below the axis of the sprocket driven by the engine. The pair of swing arms at each side of the wheel is provided with an interconnecting link with which the wheel axle structure is associated, this arrangement of parts being provided at each side of the drive wheel.
In my prior application above identified, another form of parallelogram linkage is disclosed in which the parallelogram linkage associated with the swing arms is located in a region between the periphery of the wheel and the axis of the engine sprocket, but arranged to provide an effective swing arm axis which is coincident with the axis of the engine sprocket.
The parallelogram type of linkage which has heretofore been provided in various ways, such as those referred to just above, has certain advantages in the suspension of the drive wheel of a motorcycle, including the fact that the driving chain which cooperates with the driving sprocket on the engine and the driven sprocket on the wheel has a path of substantially uniform length regardless of the degree of deflection of the driven wheel. In consequence, these parallelogram arrangements do not require any appreciable chain slack takeup when the wheel is deflected. In addition, the parallelogram linkage minimizes the torque reaction fluctuations, both with respect to the magnitude and the direction of the reaction forces delivered to the frame in different positions of deflection of the driving wheel. In this way, the torque reaction remains substantially constant for any given traction or power delivered from the wheel to the cycle frame.
The arrangement of the present invention not only provides the foregoing advantages but in addition, has additional advantages mentioned hereinafter.
In accordance with the arrangement of the present invention, the parallelogram linkage is provided in a novel manner and comprises a single swing arm at each side of the drive wheel, the arm at one side of the wheel being located at a level higher than the arm at the other side of the wheel. The ends of the swing arms at opposite sides of the wheel are interconnected through the wheel axis structure, the interconnection including an arm or lever extended upwardly from the wheel axis at one side and an arm or lever extended downwardly from the wheel axis at the other side in order to respectively cooperate with the ends of the swing arms at the opposite sides of the wheel. This swing arm interconnection provides for torsional interconnection of the arms through the axis structure. The other ends of the swing arms are pivotally mounted on portions of the frame of the motorcycle in positions on axes spaced above and below the axis of the driving sprocket.
With the arrangement just referred to, a parallelogram linkage is provided having all of the advantages hereinabove referred to but in addition, having other advantages not present in the prior arrangements. Thus, by the arrangement of the present invention, the parallelogram linkage is provided with fewer parts and much less weight than is required in the prior arrangements. This is particularly true with respect to the parts which move with the wheel, and especially because only a single swing arm need be provided at each side of the wheel.